Understanding sea level rise hazards in Hawaii

October 11, 2018

Climate change and sea level rise will increase the frequency and severity of natural hazards' impacts on our coasts from waves, storms, high tides, coastal erosion, tsunamis and flooding.

The State of Hawaii is especially vulnerable to the impacts of sea level rise with approximately 750 miles of coastline and extensive development in low-lying areas. In fact, many communities are already experiencing impacts from coastal erosion, wave run-up or flooding as a result of sea level rise. In some cases, these impacts threaten natural environments, important cultural sites, development and/or critical infrastructure (see photo on page 9).

Rapid warming of the atmosphere and oceans, caused by centuries of unabated greenhouse gas emissions, is causing increasing rates of sea level rise that are unprecedented in human history. Atmospheric concentration of carbon dioxide, a key greenhouse gas, has increased by about 40 percent since the industrial revolution and is higher than in measurements taken from ice core records of the last 800,000 years and probably as long as 4.6 million years. Global-average atmospheric temperature has increased by about one-degree celcius (1.8 degrees Fahrenheit) over the past century, closely following increases in carbon dioxide and other greenhouse gases. As a result, sea level is rising at accelerating rates around the global oceans due to thermal expansion of water and melting glaciers and ice sheets. The most up-to-date scientific literature points to three feet of sea level rise as an intermediate scenario and eight-plus feet of SLR as a worst-case scenario in this century. Further, sea level rise is projected to be higher than global averages around tropic regions, including Hawaii.

Article Photos

These images show resort properties in West Maui with temporary erosion control measures due to impacts from erosion and wave runup as a result of sea level rise and other factors. PHOTO BY TARA OWENS, UNIVERSITY OF HAWAII SEA GRANT.

Projections of global sea level rise, ranging from three feet as an intermediate scenario and eight or more feet as a worst case scenario, this century. IMAGE COURTESY OF TARA OWENS/UNIVERSITY OF HAWAII SEA GRANT COLLEGE PROGRAM.

The Sea Level Rise Vulnerability and Adaptation Report approved by the Hawaii Climate and Adaptation Commission in December 2017 provides the first statewide assessment of Hawaii's exposure and vulnerability to sea level rise, including recommendations to reduce exposure and increase capacity to adapt (see climateadaptation.hawaii.gov/wp-content/uploads/2017/12/SLR-Report_Dec2017.pdf). The Report uses 3.2 feet of sea level rise to depict hazards that may occur as early as the middle of this century. With 3.2 feet of sea level rise, it is estimated that over 6,500 structures located near the shoreline would be compromised or lost. Some of these vulnerable structures include hotels, shopping malls and small businesses. The loss of these structures may result in the interruption, relocation or even closure of those businesses. Other types of structures which may be impacted are churches, schools and community centers. In addition, houses, apartments, and condominium buildings are vulnerable, and the loss of these structures could result in over 20,000 displaced residents in need of new homes. The value of projected flooded structures, combined with the land value of the 25,800 acres projected to be flooded, amounts to over $19 billion across the state. This value does not include infrastructure such as roads and utilities; however, over 38 miles of major roads statewide may be impacted, and many utilities run parallel to or underneath these roads. For the West Maui planning district specifically, it is estimated that about 782 acres will be flooded, with an estimated economic loss of about $1.9 billion, which is the largest figure of all the Maui planning districts.

Adapting to sea level rise will make communities more resilient to both current and future natural hazards a "no-regrets" approach to adaptation. To this end, it is important to be aware of and consider the potential exposure to all natural hazards as a baseline, along with future scenarios that include additional climate change and sea level rise exposure. Property owners can use the Hawaii Sea Level Rise Viewer to look at projections of future hazard exposure and vulnerability in their community due to rising sea levels (see hawaiisealevelriseviewer.org). The viewer depicts coastal hazard exposure areas with sea level rise, including passive flooding (still water high tide flooding), and also - if appropriate supporting data exists - annual high wave flooding (over wash during the largest wave events of the year) and coastal erosion. For properties that fall within this Sea Level Rise Exposure Area (often referred to as the SLR-XA), property owners should consider adaptive measures when siting, designing, building or retrofitting habitable structures and supporting infrastructure (such as sewage disposal systems).

To learn more about environmental issues on Maui from partners within the West Maui Ridge to Reef Initiative, attend the annual Ridge to Reef Rendezvous on Saturday, Oct. 27. This family-friendly community event brings together over a dozen groups working on some aspect of stewardship from the top of the mountain to the ocean; the theme of this year's event is "2018: The International Year of the Reef." The Ridge to Reef Rendezvous features ways to get involved, a keiki fishing tournament, a "Haunted Reef" to explore, plus great food and prizes donated by generous sponsors.

Join your friends and neighbors along with scientists, managers and local conservation groups on Oct. 27 at Kahekili Beach Park (Old Airport Beach) in North Kaanapali, from 9 a.m. to noon (note: the Keiki Fishing Tournament's start time is 8 a.m.). Leading up to the weekend event, partners will host a Science Night on Wednesday, Oct. 24, at 6:30 p.m., sponsored by Kohola Brewery in Lahaina. Russell Sparks of the state Department of Land and Natural Resources' Division of Aquatic Resources will present "How are Maui's Reefs Doing?" Science Night is now open to minors if accompanied by an adult. For information, visit www.facebook.com/WestMauiKumuwai or call (808) 283-1631.

(Tara M. Owens is a coastal processes and hazards specialist with the University of Hawaii Sea Grant College Program and county Planning Department.)